Some semiconductor processes use tetraethylorthosilicate (TEOS), OMTCS or other volatile liquid precursors that are liquid at room temperature and pressure. TEOS is commonly supplied from a bubbler to a process chamber for the deposition of thin films of silicon dioxide (SiO2) on semiconductor substrates using a chemical vapour deposition (CVD) process. Within the process chamber, the TEOS dissociates in the presence of an oxygen source to form SiO2, which deposits on the substrate within the chamber.
Depending on the flow rate of the gaseous TEOS to the chamber, a waste stream drawn from the chamber by a vacuum pumping arrangement typically contains unconsumed TEOS, as well as by-products from the process within the chamber. Therefore, an abatement device is typically provided downstream from the vacuum pumping arrangement for removing TEOS from the waste stream before it is exhausted into the atmosphere.
As is known, the bubbler comprises a container for receiving TEOS from a source thereof, and into which a carrier gas, such as helium or hydrogen, is introduced. The flowing gas causes continuous evaporation of some of the TEOS, so that a gas mixture of carrier gas and vaporised TEOS is exhaust from the container to the process chamber.
In the event that the container overfills with TEOS, or if the container requires emptying for any reason, it is usual practice to dump the contents of the container into the process chamber, or into the foreline extending between the processing is being conducted within the process chamber. The discharge of TEOS in this manner can lead to random accumulation of pools of volatile, flammable TEOS within the foreline or the pumping arrangement. This can present a safety hazard, as the TEOS may react strongly with other species subsequently introduced to the process chamber, for example fluorine for chamber cleaning, or with air leaking into the pumping arrangement. In addition, random accumulation of liquid within the pumping arrangement can lead to large fluctuations in the gas flow entering the abatement device, which can be detrimental to the efficiency of the gas abatement, and hydrodynamic lock in a vacuum pump.
It is an aim of at least the preferred embodiments of the present invention to seek to solve these and other problems.